This invention relates to a signal driver circuit for a liquid crystal display ("LCD"), and more particularly, to a digital-in/analog-out signal driver circuit for controlling the gray levels of LCD pixels in LCD column driving applications.
Signal driver circuits are commonly employed with liquid crystal displays. The driver circuit typically accepts digital video data as an input and provides an analog voltage output to each particular LCD pixel column. Generally, each column in the LCD must be uniquely addressed by a signal or column driver and given the proper analog voltage in order to achieve the desired transmissivity (i.e., the desired shade of gray or color). Moreover, it is desirable that the output voltage range of a driver circuit be wide to allow for a high pixel contrast ratio.
For color LCDs, each pixel is composed of 3 sub-pixel elements representing the primary colors of red, green and blue. For example, a color VGA panel having a resolution of 640 columns .times.480 rows of uniquely addressable pixels will have 3.times.640 columns, or 1,920 columns. Typically, the signal driver circuit has one driver output for each column. Thus controlling an LCD panel requires a large number of driver outputs that consume considerable circuit area. Since circuitry size impacts the costs of a signal driver, it is desirable to reduce the size of signal drivers.
As LCD panel technology has improved, it has become desirable to render images with more continuous gray scales or to have more unique colors available. The voltage control required from signal drivers has, therefore, become more complex. However, it is also desirable to reduce the cost of a driver circuit by decreasing the physical size of the signal driver and desirable to reduce the amount of power dissipated by the driver circuit. Therefore, it is desirable to have a signal driver which balances the need for more discrete analog voltage levels while consuming less area and dissipating less power.